1. Field of the Invention
The present invention relates to a separator for fuel cells, and particularly a separator for solid-polymer electrolyte type fuel cells, which is a molded article of a carbon-phenol resin molding compound.
2. Disclosure of the Prior Art
In conventional fuel cells, a fuel gas containing hydrogen is supplied to an anode, and air containing oxygen is supplied to a cathode that is spaced away from the anode by an electrolyte film. The following electrochemical reactions happen at the anode and cathode sides, respectively.H2→2H++2e−(½)O2+2H++2e−→H2O
Therefore, this fuel cell provides electric energy according to the electrochemical reaction of H2+(½)O2→H2O.
FIG. 1 is an enlarged cross-sectional view of a solid-polymer electrolyte type fuel cell. This fuel cell comprises an electrolyte film 1 formed by an ion exchange membrane of a fluorinated resin, anode 2 and cathode 3 that are formed by a carbon cloth or a carbon paper, and a pair of separators 4 having flow channels (5, 6). The anode and cathode (2, 3) are placed at both sides of the electrolyte film 1. The separators 4 are placed on the anode and cathode (2, 3) such that the fuel gas containing hydrogen is supplied to the anode 2 through the flow channels 5 of one of the separators and the air containing oxygen is supplied to the cathode 3 through the flow channels 6 of the other separator. For the separators used in the conventional fuel cells, electrical conductivity and gas impermeability are important characteristics. For example, as described in Japanese Patent Early Publications No. 11-195422, No. 2000-21421, and No. 2000-77079, it has been proposed to use a molded article of a molding compound containing a carbon powder and a phenol resin as the separator.
However, in the conventional separators, there is a problem that electrical properties such as volume resistivity are not sufficiently satisfied. That is, as a content of the carbon powder in the molding compound is increased to improve the electrical properties, a content of the phenol resin in the molding compound relatively decreases. In such a case, since a flowability of the molding compound in the molding stage lowers, there is a fear that clearances among carbon particles can not be uniformly filled with the phenol resin, so that molded articles having residual pores are obtained. As a result, this leads to a decrease in mechanical strength and deterioration in gas impermeability of the separator.